Metabolic In Vivo Visualization of Pituitary Adenomas: a Systematic Review of Imaging Modalities

Abstract

Objective: Pituitary adenomas (PAs) are the most common intrasellar mass. Functional PAs constitute most of pituitary tumors and can produce symptoms related to hormonal overproduction. Timely and accurate detection is therefore of vital importance to prevent potentially irreversible sequelae. Magnetic resonance imaging is the gold standard for detecting PAs, but is limited by poor sensitivity for microadenomas and an inability to differentiate scar tissue from tumor residual or predict treatment response. Several new modalities that detect PAs have been proposed.

Methods: A systematic review of the PubMed database was performed for imaging studies of PAs since its inception. Data concerning study characteristics, clinical symptoms, imaging modalities, and diagnostic accuracy were collected.

Results: After applying exclusion criteria, 25 studies of imaging PAs using positron emission tomography (PET), magnetic resonance spectroscopy (MRS), and single photon emission computed tomography were reviewed. PET reliably detects PAs, particularly where magnetic resonance imaging is equivocal, although its efficacy is limited by high cost and low availability. Single photon emission computed tomography possesses good sensitivity for neuroendocrine tumors but its use with PAs is poorly documented. MRS consistently detects cellular proliferation and hormonal activity, but warrants further study at higher magnetic field strength.

Conclusions: PET and MRS appear to have the strongest predictive value in detecting PAs. MRS has the advantage of low cost, but the literature is lacking in specific studies of the pituitary. Due to high recurrence rates of functional PAs and low sensitivity of existing diagnostic workups, further investigation of metabolic imaging is necessary.

Keywords: Functional pituitary adenoma; Hormonally active pituitary adenoma; Magnetic resonance spectroscopy; Metabolic imaging; Positron emission tomography; Single photon emission computed tomography.

Figure 1

Flow chart outlining the selection process of relevant studies

Figure 2

MET-PET of an ACTH-producing PA. Before treatment with gamma-knife radiosurgery (GKRS), abnormal hypermetabolic tissue was present in the left part of the sella turcica, providing a target for GKRS (A). Decreased methionine uptake was observed in the target volume 13.5 months after GKRS treatment that normalized the 24-h cortisol urinary secretion (B). From Tang et al (2006), European Journal of Nuclear Medicine and Molecular Imaging. Used with permission.

Figure 3

MRI (A) and single-photon emission computed tomography (SPECT) using technetium-99m (Tc-99m) tetrofosmin (B) of a patient with a nonfunctional pituitary macroadenoma. From Kurtulmus et al (2007), J Endocrinol Invest. Used with permission.

Figure 4

Sagittal T2-weighted MR image (A) of a nonhemorrhagic FSH secreting pituitary adenoma, showing the position and size of the volume of interest (white rectangle) in the 1H-MRS experiment. Graph (C) revealing the water-suppressed spectra demonstrating a Cho peak typical of pituitary adenomas, fitted using LCModel (linear combination of model spectra), a user-independent frequency domain spectral fitting program (Stephen Provencher, Inc.). From Stadlbauer et al (2008), J Neurosurgery. Used with permission.